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ISSN: 2155-6180
Journal of Biometrics & Biostatistics
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Risk Score Estimation of Diabetic Retinopathy: Statistical Alte rnatives using Multiple Logistic Regression

Vaitheeswaran Kulothungan1,2*, Ramakrishnan R3, Subbiah M4 and Rajiv Raman5

1Research Scholar, Manonmaniam Sundaranar University, Tirunelvelli 627 012, Tamil Nadu, India

2National Center for Disease Informatics and Research (NCDIR), Bangalore 562 110, Karnataka, India

3National Institute of Epidemiology (ICMR), Ayapakkam, Chennai 600 077, Tamil Nadu, India

4Department of Mathematics, L.N Government College, Ponneri 601 204, Tamil Nadu, India

5Shri Bhagwan Mahavir Vitreoretinal Services, Sankara Nethralaya, 18, College Road, Chennai 600 006, Tamil Nadu, India

*Corresponding Author:
Kulothungan V, M.Sc
Scientist ‘C’ (Statistics)
National Center for Disease Informatics and Research (NCDIR)
Indian Council of Medical Research (ICMR)
Kannamangala Post, Bangalore 562 110, Karnataka, India
Tel: +91-08-28467643
Fax: +91-08-28467644
E-mail: [email protected]

Received date: November 07, 2014; Accepted date: December 23, 2014; Published date: December 31, 2014

Citation: Kulothungan V, Ramakrishnan R, Subbiah M, Raman R (2014) Risk Score Estimation of Diabetic Retinopathy: Statistical Alternatives using Multiple Logistic Regression. J Biom Biostat 5:211. doi: 10.4172/2155-6180.1000211

Copyright: © 2014 Kulothungan V, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are are credited.

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Abstract

People with type II diabetes are having more chances to develop diabetic retinopathy which is generally viewed as a multi-factorial disease. Identifying the risk of any disease, is very important for health care planning and creating score cards for identifying the risk of any disease is pervasive in medical diagnostics. This involves statistical techniques using parameter estimation of multivariable models such as linear regression, logistic regression or Cox proportional hazards regression. Geographic and/or disease specific methods for risk score estimation provide a scope to develop and evaluate new possible statistical methods for risk score analysis. This work explores the weighted scoring procedure through logistic regressions to develop two methods using Wald statistic and maximum regression coefficient by precluding the selection of protective risk factors. Further, to avoid the numerical errors due to interim rounding of digits in any computations the study includes a standard method that avoids such rounding of digits. Three widely applicable methods for score estimation of different diseases have also been considered for comparative study. All these methods are applied to Sankara Nethralaya Diabetic Retinopathy Epidemiology and Molecular Genetics Study III, a cross-sectional study to estimate the prevalence and risk factors for diabetic retinopathy in rural south India and then validated by comparing with methods used in Australian Type 2 Diabetes Risk Assessment Tool. Results have indicated that the new methods are more suitable in score estimation for diabetic retinopathy by considering the statistical property of the methods.

Keywords

Diabetic retinopathy; Logistic regression; Risk score; Wald statistic; Weighted scores

Introduction

Standardized risk score systems are used to create a system which aid in early diagnosis of a disease. Classifying individuals at risk for any disease would promote the efficiency of health system. This is relevant in Diabetes, as with these scores one could accurately predict complications and prevent their progression [1]. The epidemic of Diabetes Mellitus (DM), in particular type 2 diabetes mellitus, is assuming significant proportion in developing countries, such as India [2,3]. International Diabetes Federation (IDF) has projected that number of people with diabetes in India would rise from 65.1 million in 2013 to 109 million in 2035 [4].

Diabetic retinopathy (DR) is the most common ocular complication of diabetes. Blindness due to retinopathy is the major disability in patients with diabetes [5]. DR is often asymptomatic until a significant structural and irreversible damage occurs. Late diagnosis of DR results in significant socio-economic burden to the patient [6]. Several studies have shown that early and regular fundus examinations are important in screening, diagnosing, and monitoring DR [5-7]. Recently, risk scores for diabetes retinopathy based on anthropometric, demographic and clinical variables have been suggested to screen for DR [8,9]. However, a common risk score cannot be applied for all populations due to ethnicity differences.

Many alternative methodologies have been tried to estimate the risk score by assigning the different types of weighing procedure through logistic regression [10,11]. These scoring systems are developed using the parameters which are found to be significant at 20% level through the multiple logistic regression using stepwise backward elimination. Subsequently, the score systems are scaled in the different adoptable measures such as by multiplying the regression coefficients by 10 and rounding to the nearest integer [12,13]. By doing so, the constant corresponded to one point in the risk score system.

For each risk factor, its distance from the base category in regression coefficient units is divided by this constant and rounded to the nearest integer to get its point value [13]. Then, by dividing the coefficient for each variable in the final model by the lowest coefficient, then multiplying by 2 (all factors are significant) and rounding to whole number, a component is obtained [14]. Similarly, by dividing coefficients by the absolute value of the smallest coefficient in the model and rounding up to the nearest integer, another component is obtained. The overall risk score is calculated by adding each component together from the half sum of the two smallest coefficients in the model [15,16].

With these collective observations among the available methods, this study aims to identify suitable alternatives using statistically acceptable modifications. The objectives are (1) to address the errors due to interim rounding of digits and its impact on estimates between different weight methods; (2) to develop and validate newer methods using Wald statistic and maximum regression β-coefficient that can easily be applied to identify the risk of DR for an individual of any diversity and (3) to compare the performance of different methods through exploring different weightier procedure in developing risk score systems.

The presentation of this article is as follows: various methods for risk estimating are listed in Section 2; details of the data used in the study and the statistical analysis have been presented in Section 3 and the concluding remarks are in Section 4.

Methods for Risk Score Estimation

The general approach for developing a risk score system is explained in the context of multiple logistic regressions that has the form

equation

Where the response variable yi is a Bernoulli random variable that takes on the values either 0 or 1; equation is the observed quantities of the risk factors X1, X2,………..,Xp that can be continuous or indicator/dummy variables reflecting dichotomous risk factors or categories of risk factors; and β'=(β0, β1, β2,…….. βp) are the estimates of the regression coefficients based on the regression model; the errors (εi) has mean zero, non constant variance and need not follow normal distribution.

In order to determine points, the continuous factors (listed in X) are converted into categories based on research interest. Then, we determine the reasonable categories for each risk factor to serve as the reference category. The reference category for each risk factor is assigned as zero in the scoring system.

Scoring systems are using different types of weights Wi calculate the scores using logistic regression method, where the constant Wi is fixed to calculate the points in the score system along with βi coefficients. Table 1 shows the description of some of the existing methods that are widely applied in various medical risk estimations. Standard method (SM) provides the risk scores without any interim round off for decimal places.

Method No Extracted from Wi Range in set of integers
M1 Glumer [12] (-∞, ∞)
M2 Lei Chen [14] (-∞, ∞) –{0}
M3 Sugiokaa [15] (-∞, ∞) –{0}

Table 1: Description of existing methods which are widely applied in medical risk estimations.

The methods M1-M3 considered the β coefficient that is statistically significant in logistic modeling. The two naive approaches are M4 and M5. However, Wald statistic provides more information regarding the significance among β coefficients. Hence this work identifies a method (M4) based on Wald statistic; that is by choosing the β coefficient of risk factor correspond to highest value of Wald statistic in the output of logistic regression say βj.

Thus, Wi for method M4 in the range (-∞, ∞) will be

equation

Also compared to M2, this study has chosen max β’s instead of min |β|’s and then multiply by 100; in the M4 and M5, the βj will precludes the selection of protective factors. (i.e., negative regression coefficients). Hence Wi for method M5 is

equation

with Wi ranges over the integers from -∞ to 100; In all these methods [.] indicates the nearest integer function; accordingly [1.25]=1, [1.50]= [1.75]=2 and so on.

Subsequently, probability of the risk is computed for each factor to determine the risk of the individuals (or probability of developing an event) and is calculated as

equation

The basic idea of the point system is to approximate the contribution of the risk factors in the estimate of risk, specifically to estimate equation which is the component of each model shown above, which depends on the specific risk factor profile under consideration. The risk estimates in the points system associated with specific risk factor profiles are computed by substituting the product of the total number of points and the constant, Wi, which approximates equation into the appropriate formula (e.g. logistic regression equation) to estimate the risk.

The proposed risk score model algorithms tested for model goodness-of-fit which is evaluated using the Hosmer-Lemeshow test statistic [17] and overall predictive accuracy of the model is assessed using the c-statistic, which has similar value or equivalent to the area under the receiver operating characteristic (ROC) curve [18]. Bland and Altman test is performed to evaluate agreement between estimated risk in rounding and non-rounding methods [19]. In additional, intra class correlation coefficient (Cronbach’s alpha) is also used to assess the intersession variability [20,21]. A p value of <0.05 is considered statistical significant. All these evaluations have been implemented through the statistical software (SPSS for Windows, ver.14.0 SPSS Inc, Chicago, Il, USA).

Results

Sankara Nethralaya-Diabetic Retinopathy Epidemiology and Molecular Genetic Study (SN-DREAMS III) is a population-based, cross-sectional, study to estimate the prevalence and risk factors of diabetes and diabetic retinopathy in the South-Indian population. The detail methodology and study design of SN-DREAMS III is given elsewhere [22]. The study population is selected by multi-stage cluster sampling procedure where each cluster are having of 1,200- 2,000 population, who are selected with probability proportional to size (PPS) and the sampling weightage (reciprocal of sampling fraction) is considered into these methodologies. The diabetic retinopathy (DR) data is considered as a binary response variable (0=No DR, 1=DR) with the 12 independent variables included in the model. From the study, 1329 subjects with diabetes are included in the present study.

The risk factors have further grouped into demographic, Anthropometric measurements and biochemical factors. The demographic risk factors studied are age, gender and physical activity. Most of the studies use four groups to break the continuous variable, age; for example, 40-49, 50 to 59 years, 60 to 69 years, and 70 years. But this study has considered two categories less than 55 as younger and more than 55 as elder group. The younger age group is used as the base category. The systemic risk factors studied included the duration of diabetes mellitus, user of insulin, family history of diabetes mellitus and history of hypertension.

Anthropometric measurements, including weight and height are obtained using standardized techniques and the body mass index (BMI) is calculated using the formula: weight (kg)/height (m2). Based on the BMI, individuals are classified as lean (male<20, female<19), normal (male 20-25, female 19-24), overweight (male 25–30, female 24-29) or obese (male>30, female>29). Glycemic control is categorized as normal (HbA1c <7) and abnormal (HbA1c ≥7). High fasting plasma glucose is considered, if the value is >130 mg/dl. Anemia is defined as a hemoglobin concentration of <13 g/dl in men and <12 g/dl in women and presence of nephropathy is considered microalbuminuria if albumin creatinine ratio (ACR) is between 30 and 300 mg/g and macroalbuminuria if ACR is above 300 mg/g, respectively.

The five methods described in Section 2 have been applied to this data set; based on the objective (1), we have attempted a method without rounding the digits intermittently and have considered this approach as a SM for comparison.

Out of the 1329 individuals with diabetes, 124 (9.33%) are DR. Table 2 demonstrates the results using logistic regression models with DR as dependent variable. The model fit is found be satisfactory with overall accuracy of 91.1% along with Hosmer and Lemeshow value (χ2 =2.956, 8 d.f.) at 0.937 significance with the sensitivity 12.9% and Specificity 99.2%. Out of 12 factors, 11 are found to be risk factors for DR with statistically significant (p<0.0001) and BMI (OR: 0.37, p<0.0001) as protective factor of DR. The weight selection for M2, M3, M4 and M5 select the regression coefficient (0.304), mean of (0.304 and 0.308), highest Wald statistics corresponded regression coefficient (1.249) and highest regression coefficient (1.662) respectively. Table 3 shows the regression coefficients for the Table 2 and the points allocated to each risk factor category by difference methods for SN-DREAMS III data.

Risk factors β coefficient S.E. Wald p OR OR 95% of CI
Lower Upper
Intercept -5.281 0.019 79293 <0.0001 0.005    
Age group (<55=0 ; ≥ 55=1 ) 0.308 0.008 1473 <0.0001 1.36 1.34 1.38
Gender (female=0 ; male=1) 0.619 0.008 6058 <0.0001 1.86 1.83 1.89
Duration of DM (< 5= 0 ; ≥ 5=1) 1.249 0.008 23328 <0.0001 3.49 3.43 3.54
History of family diabetes (no=0 ; yes=1) 0.598 0.008 5542 <0.0001 1.82 1.79 1.85
User of insulin (no=0 ; yes=1) 1.662 0.018 8414 <0.0001 5.27 5.09 5.46
History of hypertension  (no=0 ; yes=1) 0.861 0.008 11869 <0.0001 2.36 2.33 2.40
BMI (non-obese = 0; obese=1) -1.003 0.017 3326 <0.0001 0.37 0.35 0.38
Physical activity (heavy =0; moderate and less=1) 0.508 0.015 1131 <0.0001 1.66 1.61 1.71
FBS  value(< 130=0; ≥ 130 =1) 0.658 0.010 3974 <0.0001 1.93 1.89 1.97
HbA1c (=7-0=0; >7 =1) 0.677 0.009 5451 <0.0001 1.97 1.93 2.00
Anemia (no=0 ; yes=1) 0.304 0.010 937 <0.0001 1.36 1.33 1.38
Nephropathy (no=0 ; yes=1) 0.820 0.008 10884 <0.0001 2.27 2.24 2.31

Table 2: Beta coefficients from the multiple logistic regression final model predicting diabetic retinopathy for SN–DREAMS III data.

Factors Score allocated for difference  methods
SM M1 M2 M3 M4 M5
Age Group ( ≥ 55 years) 0.308 3 2 1 25 19
Gender (male) 0.619 6 4 2 50 37
Duration of DM  (≥ 5 years) 1.249 12 8 4 100 75
History of family diabetes (yes) 0.598 6 4 2 48 36
User of insulin (yes) 1.662 17 11 5 133 100
History of hypertension  (yes) 0.861 9 6 3 69 52
BMI (obese) -1.003 -10 -7 -3 -80 -60
Physical Activity (moderate and less) 0.508 5 3 2 41 31
FBS  value(≥ 130) 0.658 7 4 2 53 40
HbA1c (>7 ) 0.677 7 4 2 54 41
Anemia (yes) 0.304 3 2 1 24 18
Nephropathy (yes) 0.820 8 5 3 66 49

Table 3: The points allocated to each component of the SN–DREAMS III score.

Table 4 shows that example of few patient profiles for different methods of risk estimation. SM yields exact risk estimation and other five methods (M1–M5) provided subjective risk estimation. The patient 1 show percentage change from SM is uniformly higher in M1, M2 and M3; especially M1 has highest up to 6.9%, M2 has -12.6% and M3 has -11.1% such differences highlights the effect of selection of weights, intermittent rounding the digits. Even the patient profile has the effect of high risk factors (FBS, Insulin, HbA1c and History of family diabetes) M2 and M3 tend to decrease the risk when compared to the SM. In particular patients with all presence of all risk factors also yield a negative difference in M2. These observations are pictorially represented in Figure 1.

Example of few patient profile   Patients information Risk estimation of difference method for each patients Percentage change from SM
Age group
(<55=0 ; ≥ 55=1)
Gender
(female=0 ; male=1)
Duration of DM (< 5 = 0 ; ≥ 5=1) History of family diabetes (no=0 ; yes=1) User of insulin (no=0 ; yes=1) History of hypertension (no=0 ; yes=1) BMI (non obese = 0;obese=1) Physical activity (heavy =0; moderate and less=1) FBS value (< 130=0; ≥ 130 =1) HbA1c (≤7-0=0; >7 =1) Anemia (no=0 ; yes=1) Nephropathy (no=0 ; yes=1) SM M1 M2 M3 M4 M5 M1 M2 M3 M4 M5
Patient 1 0 0 0 0 1 0 0 0 1 1 0 1 18.8 20.1 16.4 16.7 18.8 18.9 6.9 -12.6 -11.1 0.3 0.4
Patient 2 1 0 0 1 0 0 0 0 1 1 0 0 4.6 4.8 4.1 4.2 4.6 4.6 5.8 -9.9 -8.9 0.6 1.9
Patient 3 0 1 0 0 1 1 0 0 1 0 0 1 34.1 35.9 32.9 33.4 34.3 34.0 5.3 -3.5 -1.8 0.8 0.0
Patient 4 1 1 0 1 1 0 0 0 0 1 0 0 19.5 20.1 18.6 16.7 19.6 19.6 3.0 -4.6 -14.4 0.6 0.7
Patient 5 1 1 0 0 1 1 0 0 0 1 0 1 41.7 43.0 39.9 40.6 42.0 41.9 3.1 -4.4 -2.8 0.6 0.3
Patient 6 0 1 1 0 1 1 0 0 1 0 0 1 64.3 65.0 62.3 63.1 64.6 64.2 1.1 -3.0 -1.8 0.4 -0.1
Patient 7 0 1 1 1 0 1 0 0 0 0 1 0 16.1 15.7 16.4 16.7 16.1 16.0 -2.6 1.9 3.7 0.2 -0.7
Patient 8 1 1 1 1 1 1 1 1 1 1 1 1 87.9 88.3 84.8 88.8 88.1 88.1 0.5 -3.4 1.0 0.2 0.2
Patient 9 0 0 1 0 1 1 0 0 0 0 1 1 40.5 40.6 39.9 40.6 40.5 40.2 0.2 -1.4 0.2 -0.1 -0.6
Patient 10 0 0 1 1 1 1 0 0 1 1 0 1 77.6 78.9 75.3 75.9 77.7 77.7 1.7 -3.0 -2.2 0.1 0.2
Patient 11 0 1 1 1 1 1 0 0 1 1 0 0 73.9 75.4 72.3 69.9 74.1 74.1 2.0 -2.2 -5.4 0.2 0.2
Patient 12 0 0 1 1 0 1 0 0 1 1 0 1 39.7 40.6 36.3 40.6 39.9 39.8 2.3 -8.5 2.2 0.4 0.4

Table 4: The validating different methods of risk estimation and identifying percentage change from SM using SN–DREAMS III data.

biometrics-biostatistics-risk-five-methods

Figure 1: Percentage changes of estimated risk by five methods (M1-M5) compared to the standard method (SM) using SN-DREAMS III data.

Table 5 presents the summary of difference existing between the methods (M1–M5) compared with SM using the simulated combinations of 212 possibilities. And the percentage of deviation from the SM for all other the five methods show that maximum range is goes up to 41.50% in M3 compared to M4 (2.46%) and M5 (3.50%). Similarly, the lower range for M2 is -25.04 compared to M4 (-0.78%) and M5 (-1.65%). Table 6 specifies the agreement of M1–M5 with the SM where M4 has the highest Cronbach’s alpha and intra class correlation followed by that of M5. Further depicts the nature of outliers identified using Bland- Altman test from which it can be shown that M2 has maximum outliers (7.0%), followed by M1 and M3 (6.3%), M5 (5.5%) whereas least is M4 (4.74%). This observation is further augmented by the ROC using a real data set, DR as classifier with the risk estimation of M1–M5 which illuminates that M4 and M5 are the top 2 values compared to other three methods.

Parameters Percentage changes from SM in total 212 combinations
M1 M2 M3 M4 M5
N 4096 4096 4096 4096 4096
Minimum -9.33 -25.04 -19.82 -.78 -1.65
Maximum 14.22 7.10 41.50 2.46 3.50

Table 5: Minimum and maximum value for percentage change from SM in total 212 combinations.

Methods Cronbach's Alpha Intra class Correlation Area under ROC Bland-Altman test
Estimate 95% of Confidence Interval
M1 0.9997 0.9995 0.9994 0.8059 6.30%
M2 0.9963 0.9926 0.9917 0.8043 7.00%
M3 0.9986 0.9972 0.9969 0.8024 6.30%
M4 0.9999 0.9999 0.9999 0.8098 4.70%
M5 0.9999 0.9999 0.9999 0.8076 5.50%

Table 6: Results from validation analysis for five methods (M1- M5).

Now, the M4 and M5 are found to be better than the existing methodology. In order to validate, those procedures are applied to another set of information from the research article AUSDRISK [14] to understand the effect of M4 and M5 compared to M2 originally adopted. Table 7 shows the regression coefficients from the article AUSDRISK and the points allocated to each risk factor category for the M4 and M5 are computed. Then, the Table 8 presents the percentage of changes from the SM using combinations and Figure 2 depicts the pictorial form of percentage change compared to standard method. It can observe from Table 5 that M4 and M5 have uniformly lesser difference composed to that of M2. In particular this cross validation has shown that M4 has a difference in an order of 10-6 to 10-10. However the difference to M2 has gone up to 11.2% in positive side and -8.5% in the negative side.

Factors Score allocated for difference  methods
SM M2 M4 M5
Male sex 0.586 3 42 35
Age group(35-44) 0.455 2 32 27
Age group(45-54) 0.919 4 65 54
Age group(55-64) 1.3 6 92 77
Age group(≥65) 1.645 8 117 97
SE* 0.418 2 30 25
Parental history of diabetes 0.624 3 44 37
History of high blood glucose 1.358 6 96 80
Use of antihypertensive medications 0.462 2 33 27
Current smoker 0.463 2 33 27
Physical inactivity 0.428 2 30 25
Category 2 (WC) 0.884 4 63 52
Category 3 (WC) 1.411 7 100 83
Overweight (25–< 30)# 0.569 3 40 34
Obese (30–< 35)# 1.224 6 87 72
Morbidly obese (35) 1.698 8 120 100

Table 7: The points allocated to each component of the AUSDRISK score.

Example of few patient profile Patients information Risk estimation of difference method for each patients Percentage change from SM
Male sex Age group(35-44) Age group(45-54) Age group(55-64) Age group(≥65) SE* Parental history of diabetes History of high blood glucose Use of antihypertensive medications Current smoker Physical inactivity Category 2 (WC) Category 3 (WC) Overweight (25–< 30) Obese (30–< 35) Morbidly obese (≥35) SM M2 M4 M5 M2 M4 M5
Patient 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.46 0.46 0.46 0.46 0.00 0.00 0.00
Patient 2 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0.70 0.69 0.70 0.70 -0.99 <0.0001 -0.35
Patient 3 1 1 0 0 0 0 1 0 0 1 0 0 0 0 0 1 17.39 16.49 17.39 17.56 -5.18 <0.0001 0.95
Patient 4 1 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 6.61 6.49 6.61 6.60 -1.67 <0.0001 -0.11
Patient 5 0 0 0 0 1 0 0 1 1 0 0 0 0 0 0 1 44.50 40.90 44.50 44.47 -8.08 <0.0001 -0.06
Patient 6 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 3.22 3.58 3.22 3.24 11.21 <0.0001 0.65
Patient 7 1 0 0 1 0 1 0 1 1 0 0 0 0 0 1 0 49.10 46.03 49.10 49.54 -6.25 <0.0001 0.90
Patient 8 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 26.35 23.08 26.35 26.50 -12.41 <0.0001 0.58
Patient 9 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 13.62 13.81 13.62 13.56 1.39 <0.0001 -0.44
Patient 10 0 0 0 0 0 1 1 1 1 1 1 1 0 0 1 0 61.70 56.44 61.70 61.64 -8.53 <0.0001 -0.11
Patient 11 1 0 0 1 0 1 0 1 1 1 1 1 0 1 0 0 74.73 70.81 74.73 75.07 -5.24 <0.0001 0.46
Patient 12 0 0 0 0 0 1 1 0 1 0 1 1 1 0 0 0 23.92 23.08 23.92 23.94 -3.53 <0.0001 0.08

Table 8: The validating different methods of risk estimation and identifying percentage change from SM using AUSDRISK data.

biometrics-biostatistics-risk-three-methods

Figure 2: Percentage changes of estimated risk by three methods (M2, M4, M5) compared to the standard method (SM) using AUSDRISK data.

Conclusion

The present study has considered three (M1, M2 and M3) popular methods for estimating risk for the patients of a particular disease. All these methods utilize extensively the regression coefficients of logistic regression model. Since setting score cards is considered as population disease specific, a need has been felt to establish suitable procedure, understand the limitation of existing procedures through a planned study design.

Existing methods are not effective to capture the risk estimation due to various barriers. This study has aimed to consolidate few widely applied methods on risk score systems and device two new methods (M4 and M5). Further, standard method (SM) has been included in the study that is based on non-rounding the digits in the interim computations. This is extended to a comparative study with the existence and two different methods (M4 and M5).

In M4 coefficients that indicate the higher significance risk factors among statistically significant variables using Wald Statistics are obtained from the output of logistic regression modeling. Also in the method M5 the highest positive regression coefficient has been selected for score calculation. Both notions are to strengthen the risk score calculations that are indicated by the underlying variables of the regression model. All these procedures are applied to a crosssectional study to estimate the prevalence and risk factors for diabetic retinopathy in rural south India, SN–DREAMS III.

From the results it could be observed that methods M4 and M5 are more appropriate in the score card development for identifying the risk factors involved in DR. The result have further indicated that

• Notable differences exist among the methods M1, M2, M3, but not in M4, M5.

• M3 records the highest difference and M4 has the least.

• Such differences yield a reversal estimation patterns within M2 or M3.

• High risk patient’s profile has been estimated as a lower level and vice versa, when M2 and M3 are applied.

Also the methods have been cross validated using another data set from AUSDRISK [14] that also supports the above observations. By considering few statistical properties such as the choice weights, sampling techniques, and validation procedures, the present work has observed that M4 and M5 could be more suitable methods for score estimation in diseases like diabetic retinopathy. Similar attempts would help to investigate the usefulness of methods for risk score estimation involved in other diseases and different geographic locations.

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